国产SA-508Ⅲ低合金钢在模拟核电高温水服役环境中的应力腐蚀破裂及力学行为

Stress Corrosion Cracking and Mechanical Behaviors of Domestic Low Alloy Steel SA-508Ⅲ in Simulated PWR Primary Water Environment

采用慢应变速率拉伸试验(SSRT)和电化学控制结合的方法,研究了国产核电压力容器用钢SA-508Ⅲ(含S0.0025%)在模拟压水堆一回路290℃高温高压水质环境中的应力腐蚀破裂(SCC)及力学行为。电位范围从-720～+400 mV(SHE),模拟从低氧含氢的理想状态到溶解氧显著超标状态的一系列服役环境。研究结果表明,随着电极电位的升高,该材料发生SCC的敏感性升高。当电极电位处于-720～200mV(SHE)范围时,材料无SCC;电位在-50～+200mV时,发现有疑似轻微SCC迹象;而当电位升高到+300～+400 mV时,材料发生显著的SCC。扫描电镜断口观察表明,SCC裂纹通常在试样表面的夹杂物处萌生,并以准解理穿晶模式呈扇形扩展。结果显示出该材料抗SCC能力优秀,在良好水化学条件下应无明显的SCC,其SCC破裂机理应该属于阳极溶解机制。从试样拉伸曲线上可观察到锯齿状波形,显示出动态应变时效(DSA)的微观形变特征。探讨了材料DSA对SCC行为的影响。

The stress corrosion cracking （SCC） and mechanical behaviors of homemade low alloy steel SA-508 Ⅲ （S：0. 0025%） in simulated pressurized water reactor （PWR） primary water environment at 290℃ were studied by slow strain rate test （SSRT） technique. The tests were mainly performed in the water at various applied electrode potentials in the range from-720 mV to ＋ 400 mV （SHE） which simulated the electrochemical conditions of the steel in the water environment with different dissolved oxygen and hydrogen contents. A test was also performed in pure nitrogen gas for comparison. Results showed that the susceptibility to SCC of the steel increased with increasing electrode potential. No apparent SCC was found on the specimens tested at the potentials in the range from --720 mV to -200 mV （SHE）. Some signs like tiny SCC were observed on the specimens tested at -50 mV and ＋200 rnV （SHE）. Significant SCC happened when the potential was raised to ＋300 mV and ＋400 mV （SHE）. The cracks were nucleated at inclusions and propagated in fan-shaped quasi-cleavage transgranular mode. Results suggest that the steel has excellent resistance to SCC. All the tensile curves of the tests exhibited the character of dynamic strain ageing （DSA）. The SCC mechanism and its relation to DSA are discussed.